(Parts of this background may or may not constitute prior art.)
Aerial distribution cables are desirable for use in fiber-to-the-home, fiber-to-the-premises, or fiber-to-the-node broadband communications networks. These are especially worthwhile in construction of such high-speed networks in small towns and rural areas, where communications services are most economically provided using an existing aerial right of way.
Traditional loose tube or central core optical cables are relatively bulky and heavy, and can be difficult to install and handle at closures, junction boxes, etc, where the cable jacket may need to be stripped for routing of fibers and cables. Furthermore, if the cables are large and heavy it may be necessary to reinforce or replace existing telephone poles to support the added weight of the optical distribution cable. Last, the tubes of a loose tube cable or ribbons in a central core ribbon cable can be difficult to route inside closures. Loose buffer tubes tend to be stiff and hard to bend, while ribbons have a preferential bend that can make them difficult to route.
For loose tube cable designs, stiff thin-walled plastic tubes are often used. These stiff tubes, typically made out of a polymer like polybutylene terethphalate (PBT), are larger than the desired size of the cable units, and are prone to kinking permanently when handled. In some cases, it is necessary to remove the stiff buffer tube and route the relatively fragile optical fibers in a more flexible tube. Such practices add to the time and expense of deploying optical broadband distribution networks.
Another approach to reducing the size and weight of aerial cables is to use cables containing thin walled, soft ‘microsheath’ tubes to bundle the fibers, as disclosed in U.S. Pat. Nos. 6,334,015 and 7,082,241 by Sagem S A, to bundle the optical fibers. The softer tubes may meet the desired compact size of the units, but these tubes typically contain filling compound, which must be cleaned, and is an annoyance to installers. In addition, the soft microsheath tube material sometimes tends to stick to the overextruded cable sheath. When that occurs, and an installer attempts to remove cable sheath, the microsheath tube material may be inadvertently removed or torn thereby exposing the fibers and making it more difficult to determine which fiber is which. Barrier tapes or other protective materials may be included in the cable sheath structure to help prevent damage to the microsheath tubes, but this adds to the cost and complexity of the cable.
An alternate solution that has been used in some European countries is to first aerially install lightweight microduct, then later install air-blown cabled fiber units (often referred to as ABFUs) such as OFS's AccuBreeze™ or many similar commercially-available products in the microduct later. However this is inefficient, as two different installation steps are required. Also, there is a limit to the amount of fiber that can be installed in the conduit, as current commercially available ABFUs are limited to fiber counts of 12.
Thus there is a need for improved lightweight, compact, aerial cables with high fiber counts that can be installed easily in one operation.